1. Field of the Invention
The present invention relates to a positioning apparatus for positioning a slide body used in a precision machine such as, for example, an optical disc mastering machine or a semiconductor testing machine, and a frictional reciprocating drive mechanism used for reciprocatingly driving the slide body.
2. Description of the Prior Art
In a machine such as, for example, an optical disc mastering machine or a semiconductor testing machine, which requires a high precision, a pneumatic slide device in which a slide body is installed for reciprocating movement through an externally pressurized linear bearing assembly has hitherto been employed largely. For driving the slide body, a linear motor of a voice-coil type is generally employed and a closed loop control system is employed in which an interference laser measuring instrument or a linear scale is employed for a position detector. Also, in an apparatus such as, for example, the semiconductor testing machine, in which after having been positioned the slide body is required to be held in a static condition in order for a work to be observed, a ball screw is largely employed for driving the slide body.
It has, however, been found that the slide device utilizing the linear motor of the voice-coil type is of a completely non-contact design, the slide device tends to be adversely affected by an external disturbance. For this reason, improvement in resolution has hitherto been limited. On the other hand, the slide device utilizing the ball screw for driving the slide body, the presence of an error in shape of a helical groove and/or diameter of balls tends to result in fluctuation in speed so as to bring about a shaking motion of the slide body in a direction axially of a shaft.
Apart from the above, a frictional reciprocating drive mechanism comprising a main shaft adapted to be rotated and a roller held in a rolling contact with the main shaft and inclined a predetermined angle relative to the main shaft has been suggested as a device effective to accomplish a precise feed. However, even this frictional reciprocating drive mechanism is unable to accomplish a highly accurate drive of the main shaft, failing to achieve a precise positioning of the slide body, because of the presence of an influence brought about by a fluctuated rotation of the motor and/or a phase deviation occurring in a transmission system for transmitting the rotation of the motor to the main shaft.
In addition, the conventional externally pressurized linear bearing assembly has been found difficult to secure a sufficient rigidity of the bearing assembly and the lack of a sufficient rigidity tends to adversely affect the accuracy of positioning.
The apparatus in which the pneumatic slide device having the linear motor of the voice-coil type discussed above is utilized, or the apparatus in which the ball screw is utilized to drive the slide body, inherently involve a factor such as, for example, a yawing that tends to reduce the accuracy and, therefore, a highly accurate positioning is difficult to achieve.
Yet, since the accuracy of positioning is limited because of fluctuation in speed of movement of the slide body, a high density write-in is difficult to achieve where the pneumatic slide device is utilized.